U.S. patent application number 13/194604 was filed with the patent office on 2013-01-31 for circuit with a temperature protected electronic switch.
This patent application is currently assigned to Infineon Technologies Austria AG. The applicant listed for this patent is Robert Illing. Invention is credited to Robert Illing.
Application Number | 20130027830 13/194604 |
Document ID | / |
Family ID | 47503334 |
Filed Date | 2013-01-31 |
United States Patent
Application |
20130027830 |
Kind Code |
A1 |
Illing; Robert |
January 31, 2013 |
Circuit with a Temperature Protected Electronic Switch
Abstract
A method can be used for driving an electronic switch integrated
in a semiconductor body. A first temperature is measured at a first
position of the semiconductor body. A temperature propagation is
detected in the semiconductor body. The electronic switch is
switched off when the temperature at the first position rises above
a first threshold that is set dependent on the detected temperature
propagation.
Inventors: |
Illing; Robert; (Villach,
AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Illing; Robert |
Villach |
|
AT |
|
|
Assignee: |
Infineon Technologies Austria
AG
Villach
AT
|
Family ID: |
47503334 |
Appl. No.: |
13/194604 |
Filed: |
July 29, 2011 |
Current U.S.
Class: |
361/103 |
Current CPC
Class: |
H03K 2017/0806 20130101;
H02H 5/044 20130101; H03K 17/0822 20130101; H02H 7/222
20130101 |
Class at
Publication: |
361/103 |
International
Class: |
H02H 5/04 20060101
H02H005/04 |
Claims
1. An electronic circuit, comprising: an electronic switch
integrated in a semiconductor body and having a control terminal;
and a drive circuit coupled to the control terminal and comprising
a temperature protection circuit, the temperature protection
circuit comprising: a first temperature sensor having a first
sensor element located at a first position on the semiconductor
body, the first temperature sensor configured to provide a first
temperature signal that is representative of a temperature at the
first position; and a temperature propagation detection circuit
that is configured to detect a temperature propagation in the
semiconductor body and that is configured to provide a temperature
propagation signal; wherein the temperature protection circuit is
configured to switch the electronic switch off, when the
temperature at the first position rises above a first threshold;
and wherein the first threshold is dependent on the temperature
propagation signal.
2. The electronic circuit of claim 1, wherein the temperature
propagation detection circuit further comprises a second
temperature sensor, the second temperature sensor having a second
sensor element located at a second position remote to the first
position and the second temperature sensor configured to provide a
second temperature signal that is representative of a temperature
at the second position.
3. The electronic circuit of claim 2, wherein the temperature
propagation detection circuit is configured to generate the
temperature propagation signal dependent on a difference between
the first temperature signal and the second temperature signal.
4. The electronic circuit of claim 2, wherein the semiconductor
body comprises a first active area in which the electronic switch
is integrated, wherein the first temperature sensor is arranged
within the first active area, and wherein the second temperature
sensor is arranged outside the first active area.
5. The electronic circuit of claim 2, wherein the temperature
protection circuit further comprises a third temperature sensor
having a third sensor element located at a third position remote to
the first position and the second position, the third temperature
sensor configured to provide a third temperature signal that is
representative of a temperature at the third position, and wherein
the temperature protection circuit is further configured to switch
the electronic switch off, when a temperature difference between a
temperature at the first position and a temperature at the third
position rises above a second temperature threshold.
6. The electronic circuit of claim 5, wherein the semiconductor
body comprises a first active area in which the electronic switch
is integrated, wherein the first temperature sensor is arranged
within the first active area, and wherein the second temperature
sensor is arranged outside the first active area, and wherein the
third temperature sensor is arranged outside the active area and
arranged more distant to the active area than the second
temperature sensor.
7. The electronic circuit of claim 5, wherein the second
temperature threshold is dependent on the temperature propagation
signal.
8. The electronic circuit of claim 5, wherein the temperature
propagation detection circuit is configured to generate the
temperature propagation signal dependent on a difference between
the first temperature signal and the second temperature signal.
9. The electronic circuit of claim 8, wherein the temperature
protection circuit is configured to decrease the first threshold
when the difference between the first temperature signal and the
second temperature signal increases and/or when the difference
between the first temperature signal and the second temperature
signal rises above a temperature difference threshold.
10. The electronic circuit of claim 5, wherein the temperature
propagation detection circuit is configured to generate the
temperature propagation signal dependent on a difference between
the second temperature signal and the third temperature signal.
11. The electronic circuit of claim 10, wherein the temperature
protection circuit is configured to decrease the first threshold
when the difference between the second temperature signal and the
third temperature signal increases and/or when the difference
between the second temperature signal and the third temperature
signal rises above a temperature difference threshold.
12. The electronic circuit of claim 1, wherein the electronic
switch comprises a MOSFET.
13. The electronic circuit of claim 1, wherein then first sensor
element is implemented as a diode, a resistor, or a bipolar
transistor.
14. A method for driving an electronic switch integrated in a
semiconductor body, the method comprising: measuring a first
temperature at a first position of the semiconductor body;
detecting a temperature propagation in the semiconductor body; and
switching off the electronic switch, when the temperature at the
first position rises above a first threshold, wherein the first
threshold is set dependent on the detected temperature
propagation.
15. The method of claim 14, further comprising measuring a second
temperature at a second position of the semiconductor body remote
to the first position.
16. The method of claim 15, wherein detecting the temperature
propagation comprises evaluating a difference between the first
temperature and the second temperature.
17. The method of claim 15, wherein the semiconductor body
comprises a first active area in which the electronic switch is
integrated, wherein the first position is within the first active
area, and wherein the second position is outside the first active
area.
18. The method of claim 15, further comprising: measuring a third
temperature at a third position remote to the first position and
the second position; and switching off the electronic switch, when
a temperature difference between the first temperature and the
second temperature rises above a second temperature threshold.
19. The method of claim 18, wherein the semiconductor body
comprises a first active area in which the electronic switch is
integrated, wherein the first position is within the first active
area, wherein the second position is outside the first active area,
and wherein the third position is outside the first active area and
more distant to the first active area than the second position.
20. The method of claim 19, wherein the second temperature
threshold is set dependent on the detected temperature
propagation.
21. The method of claim 19, wherein detecting the temperature
propagation comprises evaluating a difference between the first
temperature and the second temperature.
22. The method of claim 21, wherein the first threshold is
increased when the difference between the first temperature and the
second temperature increases and/or when the difference between the
first temperature and the second temperature rises above a
temperature difference threshold.
23. The method of claim 19, wherein detecting the temperature
propagation comprises evaluating a difference between the second
temperature and the third temperature.
24. The method of claim 23, wherein the first threshold is
increased when the difference between the second temperature and
the third temperature increases and/or when the difference between
the second temperature and the third temperature rises above a
temperature difference threshold.
25. The method of claim 14, wherein the electronic switch is a
MOSFET.
Description
TECHNICAL FIELD
[0001] Embodiments of the present invention relate to an electronic
circuit with a temperature protected electronic switch, and to a
method for driving an electronic switch.
BACKGROUND
[0002] Electronic switches, such as MOSFETs, IGBTs, or other types
of transistors are widely used as electronic switches for switching
electrical loads, such as motors, lamps, magnetic valves, and the
like. In these applications, the electronic switch is connected in
series with the load, where the series circuit with the electronic
switch and the load is connected between power supply terminals.
The load can be switched on and off by switching the electronic
switch on and off.
[0003] Usually, the on-resistance of the electronic switch, which
is the resistance of the electronic switch in the on-state, is
lower than the resistance of the load, so that in a normal
operation state a voltage drop across the electronic switch is
significantly lower than a voltage drop across the load, when the
electronic switch is switched on. When, however, there is a short
circuit in the load and when the electronic switch is in the
on-state, the voltage drop across the electronic switch increases
and the electric power dissipated in the electronic switch
increases. The increase in dissipated power results in an increased
temperature of the electronic switch.
[0004] According to a first approach for protecting the electronic
switch from being damaged, the temperature in the electronic switch
may be detected and the electronic switch may be switched off when
the temperature reaches a given temperature threshold.
[0005] According to a second approach, a first temperature in the
electronic switch and a second temperature remote to the electronic
switch may be measured and the electronic switch may be switched
off when the difference between these two temperatures reaches a
given temperature difference threshold. Both, the first and the
second approach can be applied together.
[0006] There is a need for an improved temperature protection of an
electronic switch.
SUMMARY OF THE INVENTION
[0007] According to a first aspect, an electronic circuit is
disclosed. The electronic circuit includes an electronic switch
integrated in a semiconductor body and having a control terminal.
The electronic switch further includes a drive circuit coupled to
the control terminal and including a thermal protection circuit.
The thermal protection circuit includes a first temperature sensor
having a first sensor element located at a first position on the
semiconductor body, where the first temperature sensor is
configured to provide a first temperature signal that is
representative of a temperature at the first position. The thermal
protection circuit further includes a temperature propagation
detection circuit that is configured to detect a temperature
propagation in the semiconductor body and that is configured to
provide a temperature propagation signal, wherein the thermal
protection circuit is configured to switch the electronic switch
off, when the temperature at the first position rises above a first
threshold, and wherein the first threshold is dependent on the
temperature propagation signal.
[0008] According to a second aspect, a method for driving an
electronic switch integrated in a semiconductor body is disclosed.
The method includes measuring a first temperature at a first
position of the semiconductor body, detecting a temperature
propagation in the semiconductor body, and switching off the
electronic switch, when the temperature at the first position rises
above a first threshold. The first threshold is set dependent on
the detected temperature propagation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Examples will now be explained with reference to the
drawings. The drawings serve to illustrate the basic principle, so
that only aspects necessary for understanding the basic principle
are illustrated. The drawings are not to scale. In the drawings the
same reference characters denote like features.
[0010] FIG. 1 illustrates an electronic circuit with an electronic
switch and a drive circuit;
[0011] FIG. 2 schematically illustrates a top view on a
semiconductor body in which the electronic switch is implemented,
and illustrates first and second positions for temperature
measurement;
[0012] FIG. 3 shows method steps of a temperature protection method
according to a first embodiment that includes detecting a
temperature propagation in the semiconductor body;
[0013] FIG. 4 illustrates method steps for detecting the
temperature propagation;
[0014] FIG. 5 illustrates an embodiment of a drive circuit that
includes a thermal protection circuit;
[0015] FIG. 6 illustrates a first embodiment of driving the
electronic switch dependent on an input signal of the drive circuit
and dependent on a thermal protection signal;
[0016] FIG. 7 illustrates a second embodiment of driving the
electronic switch dependent on an input signal of the drive circuit
and dependent on a thermal protection signal;
[0017] FIG. 8 illustrates a first embodiment of the thermal
protection circuit;
[0018] FIG. 9 schematically illustrates a top view on a
semiconductor body in which the electronic switch is implemented,
and illustrates first, second and third positions for temperature
measurement;
[0019] FIG. 10 illustrates a second embodiment of the thermal
protection circuit; and
[0020] FIG. 11 illustrates a further embodiment of the thermal
protection circuit.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0021] FIG. 1 illustrates an electronic circuit with an electronic
switch 1 and a drive circuit 2 that is configured to drive the
electronic switch 1. The electronic switch 1 has a load path and a
control terminal, where the control terminal is connected to an
output of the drive circuit 2 and receives a drive signal S.sub.DRV
from the drive circuit 2. In the electronic circuit illustrated in
FIG. 1, the electronic switch 1 is implemented as a MOSFET,
specifically as an n-type MOSFET. The MOSFET has drain and source
terminals and a gate terminal. The gate terminal is a control
terminal of the MOSFET, and a load path of the MOSFET extends
between the drain and the source terminals. It should be noted that
implementing the electronic switch 1 as an n-type MOSFET is only an
example. The electronic switch 1 could also be implemented as
another type of a MOSFET, such as a p-type MOSFET, or as another
type of transistor, such as an IGBT, a JFET, or as a BJT.
[0022] The electronic switch 1 can be employed as a switch for
switching an electrical load Z, such as a motor, a lamp an actor,
and the like. For illustration purposes, the load Z is also
illustrated (in dashed lines) in FIG. 1. The load Z is connected in
series with the load path of the electronic switch 1, where the
series circuit with the electronic switch 1 and the load Z is
connected between supply terminals for a positive supply potential
V+ and a negative supply potential or reference potential GND. In
the embodiment illustrated in FIG. 1, the electronic switch 1 is
connected in a low-side configuration, which means that the
electronic switch 1 is connected between the load Z and the
terminal for the reference potential GND. However, this is only an
example. The electronic switch 1, could also be connected in a
high-side configuration.
[0023] The drive circuit 2 is configured to switch the electronic
switch 1 on and off dependent on an input signal S.sub.IN, where
the load Z is switched on when the electronic switch 1 is in an
on-state (switched on), and where the load Z is switched off, when
the electronic switch 1 is in an off-state (switched off). When the
electronic switch 1 is switched on and when the load Z is in a
normal (faultless) operation a supply voltage that is available
between the supply terminals mainly drops across the load Z. When,
however, the electronic switch 1 is in the on-state and there is a
short circuit in the load Z, the supply voltage mainly drops across
the load path of the electronic switch 1. In this case a
significant amount of electrical power is dissipated in the
electronic switch 1, which causes a temperature of the electronic
switch 1 to increase.
[0024] The drive circuit 2 includes a thermal protection circuit,
that will be explained in further detail herein below. This thermal
protection circuit is configured to protect the electronic switch 1
from being overheated. A first embodiment of a temperature
protection method employed by the thermal protection circuit will
be explained with reference to FIGS. 2 and 3.
[0025] FIG. 2 schematically illustrates a top view of a
semiconductor body (semiconductor chip, semiconductor die) 100 in
which the electronic switch 1 is integrated. The semiconductor body
100 includes a first active region 11 in which active regions, such
as body, source and drain regions, of the electronic switch 1 are
integrated. The semiconductor body 100 further includes an outside
region 12, which is a region of the semiconductor body 100 next to
the active region 11. The outside region 12 may include a logic
circuit, such as the drive circuit 2 or parts of the drive circuit
2. P1, P2 in FIG. 2 denote first and second positions on the
semiconductor body 100. The first position P1 is arranged within
the active region 11, and the second position P2 is arranged in the
outside region 12 and remote to the active region 11.
[0026] Referring to FIG. 3, the temperature protection method
includes measuring a first temperature T1 at the first position P1
(method step 210), and switching off the electronic switch 1 when
the first temperature T1 is above a temperature threshold (method
step 220). The method further includes detecting a temperature
propagation in the semiconductor body 100 (method step 230),
specifically in the outside region 12 of the semiconductor body
100, and providing the temperature threshold dependent on the
detected temperature propagation (method step 240).
[0027] Referring to FIG. 4, the method step 230 of detecting the
temperature propagation in the semiconductor body 100 may include
measuring a second temperature T2 at the second position P2 (method
step 221), and evaluating a temperature difference between the
first temperature T1 and the second temperature T2. The temperature
difference between the first and second positions P1, P2 is a
measure for the temperature propagation in the semiconductor body
100. When, for example, a short circuit occurs in the load Z (see
FIG. 1), the temperature at the first position P1, that is within
the active area 11 of the electronic switch 1, will rapidly
increase. A delay time between the occurrence of the short circuit
and the increase of the temperature at the first position P1 is,
for example, in the range of several microseconds (.mu.s), such as
between 5 .mu.s and 15 .mu.s. The semiconductor body 100 has a
thermal impedance that influences a heat or temperature propagation
from the active region 11, where the energy is dissipated, into the
outside region 12. Since the second position P2 is arranged distant
to the active region 11, a delay time between the occurrence of the
short-circuit in the load and the time when the temperature at the
second position P2 starts to increase, is higher than at the first
position P1. Thus, at the time of the occurrence of the
short-circuit there is a high temperature difference between the
first and the second temperatures T1, T2. This temperature
difference of the first and second temperature T1, T2 is a measure
for the temperature propagation in the semiconductor body 100.
According to one embodiment, the temperature threshold is dependent
on a first temperature difference dT1 between the first and second
temperatures T1, T2. The dependency of the temperature threshold
from the temperature difference dT1 is, for example, such that
there is at least one temperature difference range of this
temperature difference dT1 in which the temperature threshold
decreases with increasing temperature difference dT1.
[0028] FIG. 5 illustrates a first embodiment of the drive circuit
2. The drive circuit 2 according to FIG. 5 receives the input
signal S.sub.IN, provides the drive signal S.sub.DRV and includes a
thermal protection circuit 3. The thermal protection circuit 3 is
configured to provide a thermal protection signal S.sub.TP, where
the drive circuit 2 is configured to generate the drive signal
S.sub.DRV dependent on the input signal S.sub.IN and dependent on
the thermal protection signal S.sub.TP. The drive circuit 2
switches the electronic switch 1 off when the thermal protection
circuit S.sub.TP indicates that the first temperature T1 at the
first position P1 has reached the first temperature threshold. This
will be explained in further detail below.
[0029] Referring to FIG. 5, the thermal protection circuit 3
includes a first temperature sensor 4 and a second temperature
sensor 5. The first temperature sensor 4 is arranged at the first
position P1 and is configured to provide a first temperature signal
S.sub.T1 that is representative of the first temperature T1. The
second temperature sensor 5 is arranged at the second position P2
and is configured to provide a second temperature signal S.sub.T2
that is representative of the second temperature T2 at the second
position P2. An evaluation circuit 6 receives the first and second
temperature signals S.sub.T1, S.sub.T2 and generates the thermal
protection signal S.sub.TP.
[0030] FIG. 6 illustrates a first embodiment of generating the
drive signal S.sub.DRV and driving the electronic switch 1
dependent on the input signal S.sub.IN and the thermal protection
signal S.sub.TP. In this embodiment, the drive circuit 2 includes a
logic gate 21, such as an AND gate, that receives the input signal
S.sub.IN and the thermal protection signal S.sub.TP. The drive
signal S.sub.DRV is available at an output of the logic gate 21,
wherein optionally a driver 22 is connected downstream the logic
gate 21. The driver 22 is configured to amplify a logic signal
available at the output of the logic gate 21 to a signal level that
is suitable for driving the electronic switch 1.
[0031] The drive signal S.sub.DRV assumes one of an on-level and an
off-level, where the electronic switch 1 is switched on when the
drive signal S.sub.DRV assumes an on-level, and where the
electronic switch 1 is switched off when the drive signal S.sub.DRV
assumes an off-level. Equivalently, the input signal S.sub.IN may
assume an on-level indicating that the electronic switch 1 is to be
switched on and an off-level indicating that the electronic switch
is to be switched off. The thermal protection signal S.sub.TP may
assume a normal level and a protection level, where the electronic
switch 1 is to be switched off when the thermal protection signal
S.sub.TP assumes the protection level, while the thermal protection
signal S.sub.TP does not influence switching of the electronic
switch 1 when it assumes the normal level. For explanation purposes
it is assumed that the on-level of the input signal S.sub.IN is a
high level (logic "1"), that the off-level of the input signal
S.sub.IN is a low level (logic "0"), that the protection level of
the thermal protection signal S.sub.TP is a low level (logic "0"),
and that the normal level of the thermal protection signal S.sub.TP
is a high level (Logic "1"). In this case, the AND gate 21
generates a low level at its output in order to switch the
electronic switch 1 off, each time the input signal S.sub.IN
assumes an off-level, and each time the thermal protection signal
S.sub.TP assumes the protection level. It goes without saying that
the on-level and off-level of the input signal S.sub.IN and the
protection level and the normal level of the thermal protection
signal S.sub.TP could also be represented by other signal levels
than explained before. In this case, the logic gate 21 has to be
adapted to the signal levels of these signals S.sub.IN,
S.sub.TP.
[0032] FIG. 7 illustrates a further embodiment of generating the
drive signal S.sub.DRV and driving the electronic switch 1
dependent on the input signal S.sub.IN and the thermal protection
signal S.sub.TP. In this embodiment, an electronic switch 23, such
as a transistor, is connected between the control terminal and one
of the load terminals of the electronic switch 1. In the embodiment
illustrated in FIG. 7 in which the electronic switch 1 is
implemented as a MOSFET, the switch 23 is connected between the
gate terminal G and the source terminal S. the switch 23 is
controlled by the thermal protection signal S.sub.TP, wherein the
switch 23 is switched on, in order to switch off the electronic
switch 1, each time the thermal protection signal S.sub.TP assumes
the protection level. In this embodiment, the protection level
S.sub.TP is, for example, a high level that is suitable to switch
the switch 23 on.
[0033] FIG. 8 shows a circuit diagram of a thermal protection
circuit 3 according to a first embodiment. In this thermal
protection circuit 3 the first and second temperature sensors 5, 6
are implemented as diodes that are forward biased. In particular,
the temperature sensors 5, 6 are implemented as bipolar transistors
connected as diodes, which means that a base terminal of each
transistor is connected to its collector terminal.
[0034] Referring to FIG. 8, the evaluation circuit 4 includes a
reference signal generator 41 generating a reference signal
S.sub.REF1 that is representative of the temperature threshold.
This reference signal generator 41 includes a series circuit with a
resistor 411 and a variable first current source 412 connected in
series with the resistor 411. The series circuit with the resistor
411 and the first current source 412 is connected between voltage
supply terminals between which a supply voltage V.sub.S is
available. The reference signal S.sub.REF1 is an electrical
potential at a circuit node between the resistor 411 and the first
current source 412. This electrical potential equals the supply
voltage or supply potential V.sub.S minus a voltage drop V411
across the resistor 411 induced by a current provided by the first
current source 412. For explanation purposes it is assumed that the
resistor 411 has a resistance that is widely independent of the
temperature. In this case, the reference signal S.sub.REF1
decreases when the current I412 provided by the first current
source 412 increases.
[0035] The evaluation circuit 4 further includes a current source
42 connected in series with the temperature sensor 5. This current
source 42 draws a current through the sensor 5, where this current
causes a voltage drop V5 across the sensor 5. The voltage across a
diode that is forward biased, such as in the temperature sensor 5
of FIG. 8, has a negative temperature coefficient, which means that
the voltage V5 decreases when the temperature increases. The first
temperature signal S.sub.T1 is a voltage at a circuit node between
the first temperature sensor 5 and the second current source 42.
This temperature signal S.sub.T1 equals the supply voltage V.sub.S
minus the voltage drop V5 across the temperature sensor 5, so that
the first temperature signal S.sub.T1 increases when the
temperature increases.
[0036] Referring to FIG. 8 the thermal protection signal S.sub.TP
is available at an output of a comparator 43 that receives the
first temperature signal S.sub.T1 at a first input and the
reference signal S.sub.REF1 at a second input. In the embodiment
illustrated in FIG. 8, the first input of the comparator 43 is an
inverting input, while the second input is a non-inverting input.
In this embodiment, the protection signal level of the thermal
protection signal S.sub.TP, which is the signal level the thermal
protection signal S.sub.TP assumes when the first temperature T1
reaches the temperature threshold or when the first thermal
protection signal S.sub.T1 reaches the reference signal S.sub.REF1,
is a low-level. In case it is desired to have a high-level of the
thermal protection signal S.sub.TP as a protection level, the
inputs of the comparator 43 have to be changed.
[0037] Referring to FIG. 8, the thermal protection circuit 3
further includes the second temperature 6 arranged at the second
position P2 of the semiconductor body 100 (see FIG. 2). Like the
first temperature sensor 5, the second temperature sensor 6 is
implemented as a bipolar diode connected as a diode. A third
current source 45 is connected in series with the second
temperature sensor 6, where the series circuit with the second
temperature sensor 6 and the third current source 45 is connected
between the supply terminals. The operating principle of the second
temperature sensor 6 is the same as the operating principle of the
first temperature sensor explained before. The second temperature
signal S.sub.T2 is available at a circuit node between the second
temperature sensor 6 and the current source 45. Like the first
temperature signal S.sub.T1 the second temperature signal S.sub.T2
is an electrical potential, where the second temperature signal
S.sub.T2 increases when the temperature at the second temperature
sensor 6 increases.
[0038] In order to adjust the reference signal S.sub.REF1 dependent
on a temperature difference between the temperatures at the first
and second temperature sensors 5, 6, the thermal protection circuit
3 includes an amplifier 44 that receives the first temperature
signal S.sub.T1 at a non-inverting input, the second temperature
signal S.sub.T2 at an inverting input and that generates an output
signal S44 which controls the current I412 provided by the first
current source 412. The output signal S44 of this amplifier 44 is
dependent on a difference between the first and second temperature
signals S.sub.T1, S.sub.T2. According to one embodiment, the
controllable current source 412 is configured to increase the
current I412, in order to decrease the reference signal S.sub.REF1,
when the output signal S44 of the amplifier, that represents the
difference between the first and second temperature signals
S.sub.T1, S.sub.T2, increases.
[0039] According to one embodiment, the current source 412 is
configured to continuously change the current I412 when the
amplifier output signal S44 changes. According to a further
embodiment, the current source is a discrete current source that
provides one of two (or more) output currents I412 dependent on the
amplifier output signal S44, where the current source 412 may
provide a first current when the amplifier signal S44 representing
the temperature difference is below a given threshold and a may
provide a second current when the amplifier signal S44 is above the
threshold.
[0040] FIG. 9 illustrates a top view on a semiconductor body 100
according to a further embodiment. In this embodiment, temperatures
at three different positions P1, P2, P3 of the semiconductor body
100 are measured. The second and the third positions P2, P3 are
positions in the outside region 12, while the first position P1 is
within the active region 11 in which the electronic switch 1 is
implemented. The third position P3 is arranged more distant to the
active region 11 than the second position P2. According to one
embodiment, the second and third positions P2, P3 are selected such
that upon occurrence of a short-circuit in the electronic switch 1
the temperature at the second position P2 rises after about 5 ms to
15 ms, while the temperature at the third position P3 rises after
between about 40 ms and 60 ms after the occurrence of the short
circuit.
[0041] A first method for protecting the electronic switch 1 using
the temperatures T1, T2, T3 obtained at the three positions P1, P2,
P3 includes: comparing the first temperature P1 with a first
temperature threshold; switching off the electronic switch 1 when
the first temperature T1 reaches or increases above the first
temperature threshold; detecting a temperature propagation in the
semiconductor body 100 based on a temperature difference between
temperatures at the second position P2 and the third position P3;
and adjusting the temperature threshold dependent on the detected
temperature propagation.
[0042] A second method for protecting the electronic switch 1 using
the temperatures T1, T2, T3 obtained at the three positions P1, P2,
P3 includes: comparing the first temperature P1 with a first
temperature threshold; comparing a temperature difference T1-T3
between the first and third temperature T1, T3 with a temperature
difference threshold; switching off the electronic switch 1 when
the first temperature T1 reaches or increases above the first
temperature threshold and/or when the temperature difference T1-T3
reaches or increases above the temperature difference threshold;
detecting a temperature propagation in the semiconductor body 100
based on a temperature difference between temperatures at the
second position P2 and the third position P3; and adjusting at
least one of the temperature threshold and the temperature
difference threshold dependent on the detected temperature
propagation.
[0043] The temperature difference between temperatures T2, T3 at
the second and third positions will be referred to as second
temperature threshold in the following. This second temperature
difference is a measure for the temperature propagation in the
semiconductor body 100. According to one embodiment, at least one
of the temperature threshold and the temperature difference
threshold is dependent on this second temperature difference T2-T3.
According to a further embodiment, the temperature difference T1-T3
between the first temperature T1 and the third temperature T3 is
used as a measure for the temperature propagation. In this case, at
least one of the temperature threshold and the temperature
difference threshold is dependent on the temperature difference
T1-T3.
[0044] FIG. 10 illustrates an embodiment of a thermal protection
circuit 3 that is configured to generate the thermal protection
signal S.sub.TP dependent on the first, the second and the third
temperature T1, T2, T3. The thermal protection circuit 3 of FIG. 10
is based on the thermal protection circuit of FIG. 8, where the
thermal protection circuit of FIG. 10 additionally includes a third
temperature sensor 7. This temperature sensor 7 is located at the
third position P3 in the semiconductor body 100 and, like the first
and second temperature sensors 5, 6, is implemented as a bipolar
transistor connected as a diode. A fourth current source 47 is
connected in series with the third temperature sensor 7, where the
series circuit with the third temperature sensor 7 and the fourth
current source 47 is connected between the voltage supply
terminals. A third temperature signal S.sub.T3 is available at a
circuit node between the third temperature sensor 7 and the fourth
current source 47.
[0045] Like in the thermal protection circuit of FIG. 8, the
thermal protection signal S.sub.TP is available at the output of
the comparator 43 that receives the reference signal S.sub.REF1
from the reference signal generator 41 and the first temperature
signal S.sub.T1. This comparator 43 will be referred to as first
comparator in the following.
[0046] Referring to FIG. 10, an amplifier 49 calculates the
difference between the second temperature signal S.sub.T2 and the
third temperature signal S.sub.T3 and provides an output signal S49
that is dependent on this difference. The amplifier output signal
S49 is received by the first current source 412 in order to adjust
the current provided by this current source 412 dependent on this
temperature difference and in order to adjust the temperature
threshold represented by the reference signal S.sub.REF1. The first
current source 412 is implemented such that the current I412
provided by this current source 412 increases when the amplifier
output signal S49 increases, so as to reduce the temperature
threshold S.sub.REF1. In the embodiment illustrated in FIG. 10, the
amplifier output signal S49 increases when the difference between
the second temperature signal S.sub.T2 of the third temperature
signal S.sub.T3 increases. The second temperature signal S.sub.T2,
like in the embodiment of FIG. 8, is available at a circuit node
between the second temperature sensor 6 and the third current
source 45. Optionally, a resistor 49 is connected between the
second temperature sensor 6 and the third current source 45,
wherein in this case the second temperature signal S.sub.T2 is
available between the further resistor 49 and the third current
source 45. This resistor 49 serves to generate an offset of the
second temperature signal.
[0047] The operating principle of the temperature protection
circuit is now explained. For explanation purposes it is assumed
that there is a short circuit in the load Z (see FIG. 7) which
causes a load current through the transistor 1 to increase and,
therefore, the temperature in the semiconductor body 100 to
increase. It is further assumed that the first comparator 43 is a
hysteresis comparator that causes the transistor 1 to be switched
off when the first temperature T1 reaches the temperature threshold
and that causes the transistor 1 to be switched on again when the
first temperature T1 falls to a temperature that corresponds to the
temperature threshold minus a hysteresis value (and when the input
signal S.sub.IN still has an on-level). For explanation purposes it
is further assumed that a short circuit occurs in the load Z (see
FIG. 7) and that the input signal S.sub.IN has an on-level during
the period of the short circuit.
[0048] Right after the occurrence of the short circuit, the
temperature at the first position P1 increases, while there is no
significant temperature increase at the second and third position
P2, P3. Thus, the temperature threshold represented by the
reference signal S.sub.REF1 has a start value. When the first
temperature T1 reaches the temperature threshold the transistor 1
is switched off. During the off-period, the first temperature T1
may decrease and the heat at the first position may propagate in
the semiconductor body 100 in the direction of the second and third
positions P2, P3. When the first temperature T1 falls to below the
temperature threshold minus the hysteresis, the transistor 1 is
again switched on. After several cycles of switching off and on the
transistor 1, the temperature at the second position P2 may
increase due to the heat propagation in the semiconductor body 100,
while the temperature at the third position P3 which is arranged
even more distant to the first position P1 is not yet influenced by
the heat propagation in the semiconductor body 100. When the second
temperature T2 increases and the third temperature T3 may not
change, the temperature difference between the second and third
temperatures T2, T3 increases, which causes the temperature
threshold to be decreased. Decreasing the temperature threshold has
the effect that the transistor 1 is switched off at lower
temperatures, which reduces a temperature induced stress of the
semiconductor body 100 and, therefore, increases the robustness of
the transistor.
[0049] Reducing the temperature threshold requires a heat
propagation from the first position P1, where the heat is
dissipated, to the second position P2, so that there is a reduction
of the temperature threshold only when the short circuit exists
long enough for the temperature to propagate from the first
position P1 to the second position P2.
[0050] Optionally, a controller 10 (illustrated in dashed lines in
FIG. 7) monitors the temperature dependent switching off and on of
the transistor 1 and switches the transistor 1 off, by setting the
input signal S.sub.IN to an off-level, when a given number of
switching cycles has been reached or when the temperature induced
switching off and on exists for longer than a given time period,
such as, for example between 200 ms and 300 ms,
[0051] FIG. 11 illustrates a further embodiment of a temperature
protection circuit. The circuit according to FIG. 11 is based on
the circuit according to FIG. 10 and further includes a second
comparator 48 that receives the third temperature signal S.sub.T3
at a non-inverting input and a signal S.sub.T1-.DELTA.REF
representing the first temperature signal S.sub.T1 minus a
temperature difference threshold signal at an inverting input. This
temperature difference threshold signal is represented by a voltage
V46 across a resistor 46 connected between the first temperature
sensor 5 and the second current source 44. The first temperature
signal S.sub.T1 is available at a circuit node between the first
temperature sensor 5 and the resistor 46, while signal
S.sub.T1-.DELTA.REF is available at a circuit node between the
resistor 46 and the second current source 44.
[0052] An output signal S48 of the second comparator 48 may assume
one of two different signal levels, namely a first signal level
when the signal S.sub.T1-.DELTA.REF is below the third temperature
signal S.sub.T3, and a second signal level when the signal
S.sub.T1-.DELTA.REF is above the third temperature signal S.sub.T3.
In the first case, a difference S.sub.T1-S.sub.T3 between the first
and third temperature signals S.sub.T1, S.sub.T3 is below the
difference threshold signal represented by the voltage V46, and in
the second case the difference S.sub.T1-S.sub.T3 between the first
and third temperature signals S.sub.T1, S.sub.T3 is above the
temperature difference threshold signal. In the first case, a
temperature difference T1-T3 between the first and third
temperatures T1, T3 is below the threshold defined by the voltage
V46, while in the second case this temperature difference T1-T3 is
above the temperature difference threshold.
[0053] In the embodiment of FIG. 11 first signal level of the
output signal S48 of the second comparator 48 is a low level (logic
"0"), while the second signal level is a high level (logic "1"). An
output signal S43 of the first comparator 43 and the output signal
S48 of the second comparator 48 are received by a logic circuit 50
that generates the thermal protection signal S.sub.TP dependent on
these comparator signals S43, S48. According to one embodiment, the
logic circuit 50 is implemented such that the temperature
protection signal S.sub.TP switches the electronic switch 1 off
when at least one of the following conditions are met: The first
temperature T1 is above the temperature threshold; the temperature
difference T1-T3 between the first and third temperatures T1, T3 is
above the temperature difference threshold. According to a further
embodiment, the logic circuit 5 includes or is implemented as an
AND gate. In this case, the electronic switch 1 is switched off
through the thermal protection signal S.sub.TP only when both of
the two conditions explained before are met.
[0054] In the circuit of FIG. 11, the current source 412 defines
the temperature threshold and the current source 44 defines the
temperature difference threshold. At least one of these current
sources 412, 44 receives the amplifier signal S49, so as to adjust
at least one of the temperature threshold and the difference
temperature threshold dependent on the temperature propagation in
the semiconductor body, where the temperature difference between
the second and third temperatures T2, T3 is a measure for the
temperature propagation.
[0055] The current source 412 of the reference signal generator 41
is, for example, implemented such that the current I412 provided by
this current source 412 increases when the amplifier signal S49
increase, so as to decrease the threshold S.sub.REF1. The current
source 44 is, for example, implemented such that the current 144
provided by this current source 44 decreases when the amplifier
output signal S49 increase. When the current 144 decreases, the
voltage drop V46 across the resistor 46 decreases, so that the
difference temperature threshold (that is represented by the
voltage drop V46) decreases. The current sources 412, 44 can be
implemented like conventional controllable current sources.
[0056] It should be noted that although the embodiments discloses
before include analog devices, such as current sources, embodiments
of the invention are not restricted to be implemented using analog
devices. Instead, embodiments of the invention can be implemented
using digital devices or using a mixed technology with analog and
digital devices as well.
[0057] Although various exemplary embodiments of the invention have
been disclosed, it will be apparent to those skilled in the art
that various changes and modifications can be made which will
achieve some of the advantages of the invention without departing
from the spirit and scope of the invention. It will be obvious to
those reasonably skilled in the art that other components
performing the same functions may be suitably substituted. It
should be mentioned that features explained with reference to a
specific figure may be combined with features of other figures,
even in those cases in which this has not explicitly been
mentioned. Further, the methods of the invention may be achieved in
either all software implementations, using the appropriate
processor instructions, or in hybrid implementations that utilize a
combination of hardware logic and software logic to achieve the
same results. Such modifications to the inventive concept are
intended to be covered by the appended claims.
[0058] Spatially relative terms such as "under", "below", "lower",
"over", "upper" and the like, are used for ease of description to
explain the positioning of one element relative to a second
element. These terms are intended to encompass different
orientations of the device in addition to different orientations
than those depicted in the figures. Further, terms such as "first",
"second", and the like, are also used to describe various elements,
regions, sections, etc. and are also not intended to be limiting.
Like terms refer to like elements throughout the description.
[0059] As used herein, the terms "having", "containing",
"including", "comprising" and the like are open ended terms that
indicate the presence of stated elements or features, but do not
preclude additional elements or features. The articles "a", "an"
and "the" are intended to include the plural as well as the
singular, unless the context clearly indicates otherwise.
[0060] It is to be understood that the features of the various
embodiments described herein may be combined with each other,
unless specifically noted otherwise.
[0061] Although specific embodiments have been illustrated and
described herein, it will be appreciated by those of ordinary skill
in the art that a variety of alternate and/or equivalent
implementations may be substituted for the specific embodiments
shown and described without departing from the scope of the present
invention. This application is intended to cover any adaptations or
variations of the specific embodiments discussed herein. Therefore,
it is intended that this invention be limited only by the claims
and the equivalents thereof.
* * * * *